We power our linux workstations, notebooks and servers (a total of
130 at the moment, growing fast) with a self-made
autoinstallation of Debian (just converting to woody, we plan to
publish it when it is ready). Our conf-update package handles the
initial installation and hardware detection and configuration as
well as upgrades, all non-interactive. Several servers (e.g.
mail, a compute server) are also handled this way.

We chose Debian years ago, because we have the full possibility to
change everything to our needs and because it is relatively easy
to do upgrades (security,...). The well tested state of each
release gives us a reassuring stable base to build our additions
and upgrades (e.g for new hardware) on.